Highly Reduced Organometallics. 4. Syntheses and Chemistry of Pentacarbonylvanadate(3-) Ion, V(CO)53-

Alkali-metal reductions of various salts containing V(CO)6- in liquid ammonia provide high yields of the “super-reduced” species V(CO)53- which contains vanadium in its lowest known formal oxidation state. Although salts of V(CO)53- containing lithium, sodium, and various onium cations rapidly decompose above 0 °C, the trianion has been isolated and characterized as rather thermally stable rubidium and cesium salts, Rb3V(CO)5 and Cs3V(CO)5. A treacherously shock sensitive potassium salt, K3V(CO)5, is also described. Treatment of liquid ammonia solutions of Na3V(CO)5 with bis(triphenylphosphin)iminium chloride and tetraphenylphosphonium chloride provides thermally unstable, ammonia-insoluble solids believed to contain V(CO)53-. These decompose on warming to room temperature to provide V(CO)5PPh3-, Main-group 4 electrophiles, including R3EX (R = alkyl, aryl; E = Sn, Pb; X = halide), react with V(CO)53- to provide moderate to high yields of the new organometallic derivatives, (R3Sn)V(CO)52- and (R3E)2V(CO)51-. The dianions are the first reported organotin derivatives containing a transition metal in a formally negative oxidation state. Reactions of V(CO)53- in liquid ammonia with weak Bronsted acids including water, ammonium cation, and acetonitrile are also described. High yields (85-95%) of V(CO)5NH3- are obtained by the treatment of V(CO)s3- in liquid ammonia with 2 or more equiv of ammonium chloride. This amine-substituted anion is quite unstable in solution at room temperature but may be isolated as thermally stable Ph4As+ or Ph4P+ salts.